OS definition

An OS (Operating System) is a kind of computer program (software) which manages the machine's computing resources and provides a software environment for other applications to run, as well as provide users software and interfaces to manage the system, settings, files, etc. Without a OS, most computers will simply do nothing until instructed some way, depending on its configuration, while making it difficult to access data and run other programs without one having to manually configure, load and instruct the machine each time. OS's basically help bridge the gap between the hardware and the users, while making it easier for developers to write programs which can run on different systems without much concern about memory addressing, the CPU's instruction set and others.

Originally human computer operators acted as the "operating system", as part of their job was to load computer programs or code in, configure the machine and help deliver work. They effectively translated tasks and managed the computer's resources. Modern OS's like Windows and Linux-based OS's are in fact software suites (multiple programs), with hardware management, emulators/software managers, drivers and often Graphical User Interfaces. Such OS's utilize virtual memory addressing as well, so software developers don't have to keep track of memory addresses besides their own, while the OS allocates memory and translates between their virtual addresses and the real ones. This can also provide security too, as the OS can easily stop rogue programs from accessing other program's memory and other hardware resources.

OS's often have relatively strict hardware requirements because of the low-level handling and bridging. They are also often released in different builds (compiled versions), to accommodate the variety of systems they're made for - particularly different CPU's which may need different "opcode", computer architecture bit widths (e.g. 64 or 32) and native hardware support. The latter is necessary as users need enough control and I/O of the computer before loading in drivers and other software; thus the OS, BIOS and bootloader programs should detect things like visual display adapters (or GPU's) and support basic protocols used natively by them.

The key part of the OS suite is the kernel (or kernels), which provides the core functions - mainly hardware and resource management and the software environment, including the rest of the OS. Such modules are often loaded first after the bootloader, and always compiled (written) strictly in the Instruction Set Architecture (CPU's language) of the host. Users and their regular programs don't typically interact directly with the kernels and most kernels do not tolerate other programs interfering with its resources.